Appendix

Singularity’s environment variables

Singularity 3.0 comes with some environment variables you can set or modify depending on your needs. You can see them listed alphabetically below with their respective functionality.

A

  1. SINGULARITY_ADD_CAPS: To specify a list (comma separated string) of capabilities to be added. Default is an empty string.
  2. SINGULARITY_ALL: List all the users and groups capabilities.
  3. SINGULARITY_ALLOW_SETUID: To specify that setuid binaries should or not be allowed in the container. (root only) Default is set to false.
  4. SINGULARITY_APP and SINGULARITY_APPNAME: Sets the name of an application to be run inside a container.
  5. SINGULARITY_APPLY_CGROUPS: Used to apply cgroups from an input file for container processes. (it requires root privileges)

B

  1. SINGULARITY_BINDPATH and SINGULARITY_BIND: Comma separated string source:<dest> list of paths to bind between the host and the container.
  2. SINGULARITY_BOOT: Set to false by default, considers if executing /sbin/init when container boots (root only).
  3. SINGULARITY_BUILDER: To specify the remote builder service URL. Defaults to our remote builder.

C

  1. SINGULARITY_CACHEDIR: Specifies the directory for image downloads to be cached in.
  2. SINGULARITY_CLEANENV: Specifies if the environment should be cleaned or not before running the container. Default is set to false.
  3. SINGULARITY_CONTAIN: To use minimal /dev and empty other directories (e.g. /tmp and $HOME) instead of sharing filesystems from your host. Default is set to false.
  4. SINGULARITY_CONTAINALL: To contain not only file systems, but also PID, IPC, and environment. Default is set to false.
  5. SINGULARITY_CONTAINLIBS: Used to specify a string of file names (comma separated string) to bind to the /.singularity.d/libs directory.

D

  1. SINGULARITY_DEFFILE: Shows the Singularity recipe that was used to generate the image.
  2. SINGULARITY_DESC: Contains a description of the capabilities.
  3. SINGULARITY_DETACHED: To submit a build job and print the build ID (no real-time logs and also requires --remote). Default is set to false.
  4. SINGULARITY_DISABLE_CACHE: To disable all caching of docker/oci, library, oras, etc. downloads and built SIFs. Default is set to false.
  5. SINGULARITY_DNS: A list of the DNS server addresses separated by commas to be added in resolv.conf.
  6. SINGULARITY_DOCKER_LOGIN: To specify the interactive prompt for docker authentication.
  7. SINGULARITY_DOCKER_USERNAME: To specify a username for docker authentication.
  8. SINGULARITY_DOCKER_PASSWORD: To specify the password for docker authentication.
  9. SINGULARITY_DROP_CAPS: To specify a list (comma separated string) of capabilities to be dropped. Default is an empty string.

E

  1. SINGULARITY_ENVIRONMENT: Contains all the environment variables that have been exported in your container.
  2. SINGULARITY_ENCRYPTION_PASSPHRASE: Used to specify the plaintext passphrase to encrypt the container.
  3. SINGULARITY_ENCRYPTION_PEM_PATH: Used to specify the path of the file containing public or private key to encrypt the container in PEM format.
  4. SINGULARITYENV_*: Allows you to transpose variables into the container at runtime. You can see more in detail how to use this variable in our environment and metadata section.
  5. SINGULARITYENV_APPEND_PATH: Used to append directories to the end of the $PATH environment variable. You can see more in detail on how to use this variable in our environment and metadata section.
  6. SINGULARITYENV_PATH: A specified path to override the $PATH environment variable within the container. You can see more in detail on how to use this variable in our environment and metadata section.
  7. SINGULARITYENV_PREPEND_PATH: Used to prepend directories to the beginning of $PATH` environment variable. You can see more in detail on how to use this variable in our environment and metadata section.

F

  1. SINGULARITY_FAKEROOT: Set to false by default, considers running the container in a new user namespace as uid 0 (experimental).
  2. SINGULARITY_FORCE: Forces to kill the instance.

G

  1. SINGULARITY_GROUP: Used to specify a string of capabilities for the given group.

H

  1. SINGULARITY_HELPFILE: Specifies the runscript helpfile, if it exists.
  2. SINGULARITY_HOME : A home directory specification, it could be a source or destination path. The source path is the home directory outside the container and the destination overrides the home directory within the container.
  3. SINGULARITY_HOSTNAME: The container’s hostname.

I

  1. SINGULARITY_IMAGE: Filename of the container.

J

  1. SINGULARITY_JSON: Specifies the structured json of the def file, every node as each section in the def file.

K

  1. SINGULARITY_KEEP_PRIVS: To let root user keep privileges in the container. Default is set to false.

L

  1. SINGULARITY_LABELS: Specifies the labels associated with the image.
  2. SINGULARITY_LIBRARY: Specifies the library to pull from. Default is set to our Cloud Library.

N

  1. SINGULARITY_NAME: Specifies a custom image name.
  2. SINGULARITY_NETWORK: Used to specify a desired network. If more than one parameters is used, addresses should be separated by commas, where each network will bring up a dedicated interface inside the container.
  3. SINGULARITY_NETWORK_ARGS: To specify the network arguments to pass to CNI plugins.
  4. SINGULARITY_NOCLEANUP: To not clean up the bundle after a failed build, this can be helpful for debugging. Default is set to false.
  5. SINGULARITY_NOHTTPS: Sets to either false or true to avoid using HTTPS for communicating with the local docker registry. Default is set to false.
  6. SINGULARITY_NO_HOME: Considers not mounting users home directory if home is not the current working directory. Default is set to false.
  7. SINGULARITY_NO_INIT and SINGULARITY_NOSHIMINIT: Considers not starting the shim process with --pid.
  8. SINGULARITY_NO_NV: Flag to disable Nvidia support. Opposite of SINGULARITY_NV.
  9. SINGULARITY_NO_PRIVS: To drop all the privileges from root user in the container. Default is set to false.
  10. SINGULARITY_NV: To enable experimental Nvidia support. Default is set to false.

O

  1. SINGULARITY_OVERLAY and SINGULARITY_OVERLAYIMAGE: To indicate the use of an overlay file system image for persistent data storage or as read-only layer of container.

P

  1. SINGULARITY_PWD and SINGULARITY_TARGET_PWD: The initial working directory for payload process inside the container.

R

  1. SINGULARITY_REMOTE: To build an image remotely. (Does not require root) Default is set to false.
  2. SINGULARITY_ROOTFS: To reference the system file location.
  3. SINGULARITY_RUNSCRIPT: Specifies the runscript of the image.

S

  1. SINGULARITY_SANDBOX: To specify that the format of the image should be a sandbox. Default is set to false.
  2. SINGULARITY_SCRATCH and SINGULARITY_SCRATCHDIR: Used to include a scratch directory within the container that is linked to a temporary directory. (use -W to force location)
  3. SINGULARITY_SECTION: To specify a comma separated string of all the sections to be run from the deffile (setup, post, files, environment, test, labels, none)
  4. SINGULARITY_SECURITY: Used to enable security features. (SELinux, Apparmor, Seccomp)
  5. SINGULARITY_SECRET: Lists all the private keys instead of the default which display the public ones.
  6. SINGULARITY_SHELL: The path to the program to be used as an interactive shell.
  7. SINGULARITY_SIGNAL: Specifies a signal sent to the instance.

T

  1. SINGULARITY_TEST: Specifies the test script for the image.
  2. SINGULARITY_TMPDIR: Used with the build command, to consider a temporary location for the build.

U

  1. SINGULARITY_UNSHARE_PID: To specify that the container will run in a new PID namespace. Default is set to false.
  2. SINGULARITY_UNSHARE_IPC: To specify that the container will run in a new IPC namespace. Default is set to false.
  3. SINGULARITY_UNSHARE_NET: To specify that the container will run in a new network namespace (sets up a bridge network interface by default). Default is set to false.
  4. SINGULARITY_UNSHARE_UTS: To specify that the container will run in a new UTS namespace. Default is set to false.
  5. SINGULARITY_UPDATE: To run the definition over an existing container (skips the header). Default is set to false.
  6. SINGULARITY_URL: Specifies the key server URL.
  7. SINGULARITY_USER: Used to specify a string of capabilities for the given user.
  8. SINGULARITY_USERNS and SINGULARITY_UNSHARE_USERNS: To specify that the container will run in a new user namespace, allowing Singularity to run completely unprivileged on recent kernels. This may not support every feature of Singularity. (Sandbox image only). Default is set to false.

W

  1. SINGULARITY_WORKDIR: The working directory to be used for /tmp, /var/tmp and $HOME (if -c or --contain was also used)
  2. SINGULARITY_WRITABLE: By default, all Singularity containers are available as read only, this option makes the file system accessible as read/write. Default set to false.
  3. SINGULARITY_WRITABLE_TMPFS: Makes the file system accessible as read-write with non-persistent data (with overlay support only). Default is set to false.

Build Modules

library bootstrap agent

Overview

You can use an existing container on the Container Library as your “base,” and then add customization. This allows you to build multiple images from the same starting point. For example, you may want to build several containers with the same custom python installation, the same custom compiler toolchain, or the same base MPI installation. Instead of building these from scratch each time, you could create a base container on the Container Library and then build new containers from that existing base container adding customizations in %post, %environment, %runscript, etc.

Keywords

Bootstrap: library

The Bootstrap keyword is always mandatory. It describes the bootstrap module to use.

From: <entity>/<collection>/<container>:<tag>

The From keyword is mandatory. It specifies the container to use as a base. entity is optional and defaults to library. collection is optional and defaults to default. This is the correct namespace to use for some official containers (alpine for example). tag is also optional and will default to latest.

Library: http://custom/library

The Library keyword is optional. It will default to https://library.sylabs.io.

docker bootstrap agent

Overview

Docker images are comprised of layers that are assembled at runtime to create an image. You can use Docker layers to create a base image, and then add your own custom software. For example, you might use Docker’s Ubuntu image layers to create an Ubuntu Singularity container. You could do the same with CentOS, Debian, Arch, Suse, Alpine, BusyBox, etc.

Or maybe you want a container that already has software installed. For instance, maybe you want to build a container that uses CUDA and cuDNN to leverage the GPU, but you don’t want to install from scratch. You can start with one of the nvidia/cuda containers and install your software on top of that.

Or perhaps you have already invested in Docker and created your own Docker containers. If so, you can seamlessly convert them to Singularity with the docker bootstrap module.

Keywords

Bootstrap: docker

The Bootstrap keyword is always mandatory. It describes the bootstrap module to use.

From: <registry>/<namespace>/<container>:<tag>@<digest>

The From keyword is mandatory. It specifies the container to use as a base. registry is optional and defaults to index.docker.io. namespace is optional and defaults to library. This is the correct namespace to use for some official containers (ubuntu for example). tag is also optional and will default to latest

See Singularity and Docker for more detailed info on using Docker registries.

Registry: http://custom_registry

The Registry keyword is optional. It will default to index.docker.io.

Namespace: namespace

The Namespace keyword is optional. It will default to library.

IncludeCmd: yes

The IncludeCmd keyword is optional. If included, and if a %runscript is not specified, a Docker CMD will take precedence over ENTRYPOINT and will be used as a runscript. Note that the IncludeCmd keyword is considered valid if it is not empty! This means that IncludeCmd: yes and IncludeCmd: no are identical. In both cases the IncludeCmd keyword is not empty, so the Docker CMD will take precedence over an ENTRYPOINT.

See Singularity and Docker for more info on order of operations for determining a runscript.

Notes

Docker containers are stored as a collection of tarballs called layers. When building from a Docker container the layers must be downloaded and then assembled in the proper order to produce a viable file system. Then the file system must be converted to Singularity Image File (sif) format.

Building from Docker Hub is not considered reproducible because if any of the layers of the image are changed, the container will change. If reproducibility is important to your workflow, consider hosting a base container on the Container Library and building from it instead.

For detailed information about setting your build environment see Build Customization.

shub bootstrap agent

Overview

You can use an existing container on Singularity Hub as your “base,” and then add customization. This allows you to build multiple images from the same starting point. For example, you may want to build several containers with the same custom python installation, the same custom compiler toolchain, or the same base MPI installation. Instead of building these from scratch each time, you could create a base container on Singularity Hub and then build new containers from that existing base container adding customizations in %post , %environment, %runscript, etc.

Keywords

Bootstrap: shub

The Bootstrap keyword is always mandatory. It describes the bootstrap module to use.

From: shub://<registry>/<username>/<container-name>:<tag>@digest

The From keyword is mandatory. It specifies the container to use as a base. registry is optional and defaults to ``singularity-hub.org. tag and digest are also optional. tag defaults to latest and digest can be left blank if you want the latest build.

Notes

When bootstrapping from a Singularity Hub image, all previous definition files that led to the creation of the current image will be stored in a directory within the container called /.singularity.d/bootstrap_history. Singularity will also alert you if environment variables have been changed between the base image and the new image during bootstrap.

oras bootstrap agent

Overview

Using, this module, a container from supporting OCI Registries - Eg: ACR (Azure Container Registry), local container registries, etc can be used as your “base” image and later customized. This allows you to build multiple images from the same starting point. For example, you may want to build several containers with the same custom python installation, the same custom compiler toolchain, or the same base MPI installation. Instead of building these from scratch each time, you could make use of oras to pull an appropriate base container and then build new containers by adding customizations in %post , %environment, %runscript, etc.

Keywords

Bootstrap: oras

The Bootstrap keyword is always mandatory. It describes the bootstrap module to use.

From: oras://registry/namespace/image:tag

The From keyword is mandatory. It specifies the container to use as a base. Also,``tag`` is mandatory that refers to the version of image you want to use.

localimage bootstrap agent

This module allows you to build a container from an existing Singularity container on your host system. The name is somewhat misleading because your container can be in either image or directory format.

Overview

You can use an existing container image as your “base”, and then add customization. This allows you to build multiple images from the same starting point. For example, you may want to build several containers with the same custom python installation, the same custom compiler toolchain, or the same base MPI installation. Instead of building these from scratch each time, you could start with the appropriate local base container and then customize the new container in %post, %environment, %runscript, etc.

Keywords

Bootstrap: localimage

The Bootstrap keyword is always mandatory. It describes the bootstrap module to use.

From: /path/to/container/file/or/directory

The From keyword is mandatory. It specifies the local container to use as a base.

Notes

When building from a local container, all previous definition files that led to the creation of the current container will be stored in a directory within the container called /.singularity.d/bootstrap_history. Singularity will also alert you if environment variables have been changed between the base image and the new image during bootstrap.

yum bootstrap agent

This module allows you to build a Red Hat/CentOS/Scientific Linux style container from a mirror URI.

Overview

Use the yum module to specify a base for a CentOS-like container. You must also specify the URI for the mirror you would like to use.

Keywords

Bootstrap: yum

The Bootstrap keyword is always mandatory. It describes the bootstrap module to use.

OSVersion: 7

The OSVersion keyword is optional. It specifies the OS version you would like to use. It is only required if you have specified a %{OSVERSION} variable in the MirrorURL keyword.

MirrorURL: http://mirror.centos.org/centos-%{OSVERSION}/%{OSVERSION}/os/$basearch/

The MirrorURL keyword is mandatory. It specifies the URI to use as a mirror to download the OS. If you define the OSVersion keyword, then you can use it in the URI as in the example above.

Include: yum

The Include keyword is optional. It allows you to install additional packages into the core operating system. It is a best practice to supply only the bare essentials such that the %post section has what it needs to properly complete the build. One common package you may want to install when using the yum build module is YUM itself.

Notes

There is a major limitation with using YUM to bootstrap a container. The RPM database that exists within the container will be created using the RPM library and Berkeley DB implementation that exists on the host system. If the RPM implementation inside the container is not compatible with the RPM database that was used to create the container, RPM and YUM commands inside the container may fail. This issue can be easily demonstrated by bootstrapping an older RHEL compatible image by a newer one (e.g. bootstrap a Centos 5 or 6 container from a Centos 7 host).

In order to use the yum build module, you must have yum installed on your system. It may seem counter-intuitive to install YUM on a system that uses a different package manager, but you can do so. For instance, on Ubuntu you can install it like so:

$ sudo apt-get update && sudo apt-get install yum

debootstrap build agent

This module allows you to build a Debian/Ubuntu style container from a mirror URI.

Overview

Use the debootstrap module to specify a base for a Debian-like container. You must also specify the OS version and a URI for the mirror you would like to use.

Keywords

Bootstrap: debootstrap

The Bootstrap keyword is always mandatory. It describes the bootstrap module to use.

OSVersion: xenial

The OSVersion keyword is mandatory. It specifies the OS version you would like to use. For Ubuntu you can use code words like trusty (14.04), xenial (16.04), and yakkety (17.04). For Debian you can use values like stable, oldstable, testing, and unstable or code words like wheezy (7), jesse (8), and stretch (9).

MirrorURL:  http://us.archive.ubuntu.com/ubuntu/

The MirrorURL keyword is mandatory. It specifies a URI to use as a mirror when downloading the OS.

Include: somepackage

The Include keyword is optional. It allows you to install additional packages into the core operating system. It is a best practice to supply only the bare essentials such that the %post section has what it needs to properly complete the build.

Notes

In order to use the debootstrap build module, you must have debootstrap installed on your system. On Ubuntu you can install it like so:

$ sudo apt-get update && sudo apt-get install debootstrap

On CentOS you can install it from the epel repos like so:

$ sudo yum update && sudo yum install epel-release && sudo yum install debootstrap.noarch

arch bootstrap agent

This module allows you to build a Arch Linux based container.

Overview

Use the arch module to specify a base for an Arch Linux based container. Arch Linux uses the aptly named pacman package manager (all puns intended).

Keywords

Bootstrap: arch

The Bootstrap keyword is always mandatory. It describes the bootstrap module to use.

The Arch Linux bootstrap module does not name any additional keywords at this time. By defining the arch module, you have essentially given all of the information necessary for that particular bootstrap module to build a core operating system.

Notes

Arch Linux is, by design, a very stripped down, light-weight OS. You may need to perform a significant amount of configuration to get a usable OS. Please refer to this README.md and the Arch Linux example for more info.

busybox bootstrap agent

This module allows you to build a container based on BusyBox.

Overview

Use the busybox module to specify a BusyBox base for container. You must also specify a URI for the mirror you would like to use.

Keywords

Bootstrap: busybox

The Bootstrap keyword is always mandatory. It describes the bootstrap module to use.

MirrorURL: https://www.busybox.net/downloads/binaries/1.26.1-defconfig-multiarch/busybox-x86_64

The MirrorURL keyword is mandatory. It specifies a URI to use as a mirror when downloading the OS.

Notes

You can build a fully functional BusyBox container that only takes up ~600kB of disk space!

zypper bootstrap agent

This module allows you to build a Suse style container from a mirror URI.

Note

zypper version 1.11.20 or greater is required on the host system, as Singularity requires the --releasever flag.

Overview

Use the zypper module to specify a base for a Suse-like container. You must also specify a URI for the mirror you would like to use.

Keywords

Bootstrap: zypper

The Bootstrap keyword is always mandatory. It describes the bootstrap module to use.

OSVersion: 42.2

The OSVersion keyword is optional. It specifies the OS version you would like to use. It is only required if you have specified a %{OSVERSION} variable in the MirrorURL keyword.

Include: somepackage

The Include keyword is optional. It allows you to install additional packages into the core operating system. It is a best practice to supply only the bare essentials such that the %post section has what it needs to properly complete the build. One common package you may want to install when using the zypper build module is zypper itself.

docker-daemon & docker-archive bootstrap agents

For users using docker locally there are two options for creating Singularity images without the need for a repository: docker-daemon:// and docker-archive://

Overview

docker-daemon allows you to build a SIF from locally running docker daemon images while docker-archive let’s you build from tar archives of images pulled from docker.

Keywords

From: /path/to/container/file/or/directory

The From keyword is mandatory and applies to these modules in the same nature as described for other Bootstrap agents.

scratch bootstrap agent

Through all the Bootstrap agents mentioned above, you were essentially building over a base(parent) image pulled from either Library/Docker/Shub/Oras etc, but Singularity offers support to create even the base images or minimal images to create your custom containers.

Overview

This module allows you to take full control of the content inside your container, i.e., the user mentions the binaries/packages required for creation of the container. The installation of any software, necessary configuration files can all be mentioned in the %setup section of the definition file. This agent is particularly useful for creating minimal image sizes and is more secure since the creator is fully aware of what’s inside the container (ideally only the items required to run your application) and hence reduces the attack surface.

Keywords

Bootstrap: scratch

Since you are building the image from scratch, it does not require and hence does not support any keywords.